We used the diffusers, several throughout the house, along with the Feliway spray and collars. There was, perhaps, a moderate effect/improvement in the aggression and spraying behaviors right after starting to use, but then things went right back to as bad as ever. Pee everywhere, growling, hissing, chasing, fighting to the point of one cat pooping. It was awful. So many folks raved, at multiple sites, about the pheromones, but it just didn't work for us, at least not enough to justify the expense. And we used it continuously for about 6 months to give it a fair trial. At any rate, after trying a very long list of products and environmental changes to improve the situation, and spending a fortune, we found relief by letting a two of the three cats go outside away from the one who just would not leave them alone, and put him on Prozac. Prozac was the absolute last resort and I know some folks say they would never ever do such a thing. But it worked.